Fuse and fuse holder



Feb. 23, 1954 Filed Oct. 9, 1952 F. J. KOZACKA FUSE AND FUSE HOLDER 3Sheets-Sheet l 1954 F. J. KOZACKA ,670,418

FUSE AND FUSE HOLDER Filed Oct. 9, 1952 5 Sheets-Sheet 2 Feb. 23, 1954J. KQZACKA 2,670,418

FFFFFFFFFFFFFFF ER Fig. 3 is a side elevation of a fuse according toFigs. 1 and 2 inserted into a fuse holder embodying this invention;

Fig. 4. is a side elevation of the structure shown in Fig. 3;

Fig. 5 is a top plan view of the structure shown in Fig. 3;

Fig. 6 is a perspective illustration of a fuse and of the right handportion of a fuse holder for extremely high currents, the identical lefthand portion of the fuse holder being omitted;

Fig. '7 is a top plan view of another combination of fuses and of a fuseholder embodying this this invention;

Fig. 8 is a cross-section along 8-8 of Fig. '7, and

Fig. 9 is partly a side elevation and partly a longitudinal section of afuse embodying the present invention.

Referring now to Figs, 1 and 2, the fuse shown therein comprises a pairof cylindrical terminal elements I preferably made of solid copper andarranged in spaced relation. Each of terminal elements l is providedWith a coaxial cylindrical projection la. forming an integral partthereof. Projections la form connectors or connector studs for insertingthe fuse into a fuse holder of the type shown in Figs. 3 to 9,inclusive. A plurality of slots lb are milled into each terminal elementl at juxtaposed surfaces thereof. The depth of slots lb may be in theorder of and the angular displacement thereof in the order of 20degrees. Each slot or groove lb is adapted to receive a plurality offuse links 2. Each of said plurality of fuse links 2 consists of aribbon of silver or copper and each such ribbon is provided with aplurality of points of reduced cross-section. The points 2a of minimumcross-section of each link 2 limit the peak of the let-through currentto a relatively low value, far below the peak of the availableshort-circuit current of 1 the circuit into which the fuse is inserted.The large mass of copper of the terminal elements l (see Fig. 1)normally absorbs and dissipates the heat generated at the points oflinks 2 of reduced cross-sectional area. Fusion of the links 2 at thepoints 2a of minimum cross-sectional area occurs upon occurrence of acurrent of shortcircuit current proportions. If it is desired to use thefuse for overload protection each of the links 2 may be provided with atin rivet 2b. Tin rivets 2b fuse upon occurrence of relatively smallprotracted overloads and the metal of which links 2 are made diffusesinto the melted tin, thus resulting in dispersal of links 2 andinterruption of the circuit. The spaces between the fuse links 2 arefilled with a pulverulent arc extinguishing substance 3, preferably purequartz sand having a grain size in the order of 50-60 U. S. sievenumber. Inasmuch as the let-through current and the are energy of thestructure of Figs. 1 and 2 are small, the quantity of filler 3 requiredis small and the volume occupied by the entire structure iscorrespondingly small.

Terminals l are securely held apart the required relatively limiteddistance by a central spacer structure. This structure includes a pairof concentric tubes 4, 5 of a material which combines high heat and heatshock resistance, mechanical strength and good insulating properties.The tubular elements 4, 5 are preferably made of a glass-cloth laminateimpregnated with a suitable synthetic resin. The radially inner tubularelement 5 is provided with a pair of metal caps 5a secured to it bysteel pins 5b and may contain a filler rod 50 of insulating. material.

Caps 5a enter cylindrical recesses lc in terminal elements I. Only theleft hand cap 5a, the left hand steel pin 5b and the left hand terminalrecess lc have been shown in Fig. l. A large amount of pressure isapplied for inserting the structure 5, 5a, 5b into the terminal elementsI, thus establishing the required high degree of dimensional stability.The links 2 and the granular arc-extinguishing filler 3 are enclosed inan insulating shell or casing E which is secured to terminals l by meansof steel pins 'l. Ferrules B of sheet metal are arranged at both ends ofthe fuse structure. It will be apparent that the cross-sectional area'ofconnector studs la is considerably smaller than the cross-sectional areaof casing 6.

Referring now to Figs. 3-5, it will be apparent from these figures thatthe pair of coaxial cylindrical connectors or connector studs Idprojecting from the fuse structure generally designated by the referenceletter F, and more particularly from the cylindrical casing 6 of thefuse structure F, have been inserted into a fuse holder particularlydesigned to receive said cylindrical connectors or connector studs. Thefuse holder comprises a pair of substantially L-shaped brackets 9 ofsolid copper arranged in spaced relation each with one shank 9a thereofin a pair of parallel planes and each with the other shank 9b thereof ina common plane. The shanks 9a are formed by substantially equilateralsquare blocks of copper substantially equal in length to the diameter ofcasing G. Shanks 9a form adivided bearing substantially equal indiameter to the diameter of the connectors or connector studs la and incooperative engagement therewith.

I Reference numberal ll] has been applied to the cylindrical bearingsurfaces which are in cooperative engagement with connector studs la.The clamping screws H are secured to the lower portions of the dividedbearings and pass loosely through bores l2 provided in the upperportions or bearing caps thereof. Nuts l 3 enable to clamp firmly thebearing surfaces ll) in the upper and lower portions of the dividedbearings against the cylindrical connector studs la, thus ensuring theamount of contact pressure required to minimize 1 -1 losses at thecontacts. A small gap 2%) is always present between the upper portion orbearing cap and the lower portion of each contact bearing.

As nuts l3 are being tightened initially two opposite line contacts areestablished between the surface of each connector stud la and eachbearing surface It]. Further tightening of nuts l3 increases the contactpressure prevailing at these two substantially linear contacts of eachconnector stud la but simultaneously each connector stud la is beingdeformed and engages the bearing surfaces l8 under pressure atprogressively increasing areas. With further increase of contactpressure the deformation of the connector studs la progresses and thecontact area changes accordingly from the above referred to initial pairof linear contacts to a surface type or butt contact, i. e. current isthen transmitted along substantially the entire peripheral surface ofstuds la. Since the surface type or butt contacts involve a largercontact area and a higher contact pressure than the linear contactsformed during the initial stages of the tightening process of thecontact bearing, it is readily apparent that the surface or buttcontacts involve relatively less 1 -1 losses than the linear contactarrangement of which they are an out.- srowth.

It will also be read y apparent from Fi s. 3 9 hat the renewal of a newfuse for a blown fuse is a simple matter of loosening and tightening buta few screws. In prior art fuses and fuse. holder structures having acomparable current rating. 1. e. a currenpcarrying, capacity in theorder of several thousand amperes. the bladecontacts of the fuse had tobe secured directly to the bus bars. This involved loosening andtightening 01'. a much. larger number of screws. It takes therefore muchmore time and effort to renew prior art fuses than fus s according tothis invention,

As shown in Figs. 3 to 5.. inclusive. the shanks a r brackets 9 are eachprovided with a. plurality of transverse bores or holes 14. Thesetransverse bores or holes M are adapted for attachment f the fuse holderand the fuse F to a system of spaced bus bars shown at 15'.

It will be apparent froms Figs. 3 to 5-. inclusive. that the shanks 9a.of the two substantially L.- shapcd fuse holder brackets 9 which arearranged. n a pair of parallel planes are spa ed a distance slightly inexcess of the length of the casing 6 of fuse .F. Ea h bracket 9 isarranged with the other shank 9b thereof a common plane at right anglesto the above pair of parallel, planes. The shanks 9c are formed bysubstantially equilateral sq are blocks substantially equal in. lengthto the diameter of the casing G of fuse F. These. square blocks are eachsubdivided. into two parts to form. a divided contact bearing having acylindrical bearing surfa e to su stantially equal in diameter to the.diameter of connector studs la.

The structure shown in Fig. 6 is substantially the same as that shown inF gs. 3 to 5 xcept that the former is provided with two pairs of para elshanks 9a, 9a of which only one is shown in the drawing. Each pair ofshanks 9c. 8c is arranged in. a separate pair of par ll l planes andeach pair of shanks 9a, 9a forms a pair of divided bearings for theconnector studs la.

The structure of Figs. d and 8 is adapted to accommodate av pair of highcurrent-carrying capacity fuses F and F" instead of merely one suchfuse. The four parallel shanks 9a are designed to form each a contactbearing. Each pair of four contact bearings formed by shanks 9aaccommodates one pair of Connector studs la.

The right hand shank 9b and the left hand shank 9b each support one pairof shanks 9a, e. each shank 9b is common to a. pair of shanks 9a. Shanks9b are provided with a plurality of transverse bores l4 adapted toattach the fuse holder to a system of spaced bus bars (not shown).

Fig. 9 shows a high current-carrying and high interrupting capacity fusesimilar to that shown in Figs. 1 and 2. The fuse comprises a casing 6and a pair of coaxial cylindrical connector studs la projecting fromopposite ends of easing 6. The connector studs la are hollow, at leastin part, to increase the ratio of surface to crosssectional area, thustending to increase the rate at which watt-losses within the fuse arebeing dissipated. As clearly shown in Fig. 9 that portion of connectorstuds Ia which is situated at the ends thereof remote from casing 6 ishollow. The portions of the studs la immediately adjacent casing 6 aresolid. It is apparent that hollow connector studs will not only bebetter heat exchangers or heat dissipaters than solid studs, but willtend to be more readily deformed by the clamping pressure and hence tendto establish a better contact with any of the fuse holders shown,

i. e. either that shown in Figs. as. that shown in Fig. 6, or that shownin Figs. 7 and. &

It will be. understood that by illustrating several preferred forms offuse structures and fuse holder structures, I do not intend to limit myinvention thereto. It will further be understood that while thearrangements described. and illustrated herein are. the preferredembodiments of my invention, the same may take forms other thanspecifically shown and described herein. It will; be apparent for thoseskilled in the art that various changes and modifications may be madewithout departing hum the spirit of the inven tion or from the scope ofthe appended claims,

It is claimed and desired to secure by Letters Patent:

1. A structure including a cartridge type hizh current carrying capacityfuse comprising a casing having a relatively large cross-sectional areaand a pair of coaxial cylindrical connector studs having a relativelysmall cross-sectional area pro- J'ecting from opposite ends. of saidcasing, and a fuse holder adapted to support said fuse and to receivesaid pair of connector studs of said fuse, said fuse holder comprising apair of supports spaced 2. distance substantially equal to the length ofsaid casing of said fuse, each of said pair of supports forming a.divided bearing having a cylindrical bearing surface engaging one ofsaid pair of connector studs of said fuse and having clamping means forexerting clamping pressurein a direction transversely of said casing andsaid pair of connector studs for firmly clamping said 7 bearing surfaceagainst said one of said pair of connector studs of said fuse.

2. A structure according to claim 1 wherein each of said pair ofcylindrical connector studs is hollow at the portion thereof remote fromsaid casing of said fuse.

3. A structure including a cartridge type high current-carrying capacityfuse comprising a cylindrical casing having a. relatively largecrossscctional area and a pair of cylindrical connectorstuds having arelatively small cross-sectional area arranged coaxially with respect tosaid casing and projecting from opposite ends thereof, and a fuse holdercomprising a pair of fuse supports consisting of a pair ofsubstantially- L-shaped brackets spaced a distance slightly in excess ofthe length of said casing, said pair of brackets forming a pair ofdivided bearings having substantially cylindrical bearing surfaces, saidbearing surfaces having an internal diameter substantially equal to thediameter of said pair of connector studs, and each of said pair ofconnector studs being conductively engaged under pres sure by one ofsaid bearing surfaces.

4. A structure including a cartridge type high current-carrying capacityfuse comprising a cylindrical casing having a relatively largecrosssectional area and a pair of cylindrical connector studs having arelatively small cross-sectional area arranged coaxially with respect tosaid casing and projecting from opposite ends thereof, and a fuse holdercomprising a pair of substantially L-shaped brackets, each of said pairof brackets being arranged with one shank thereof in a pair of parallelplanes spaced a distance slightly in excess of the length of said casingof said fuse, and each of said pair of brackets being arranged withanother shank thereof in a common plane, each shank of said pair ofbrackets arranged in said pair of parallel planes forming a dividedbearing including a bearing cap and cap screws and having a cylindricalbearing surface cooperating with one of said pair' of con'n'ect'or'studs, and each shank of said pair of brackets arranged in said commonplane being provided with means for attachment to a system of spaced busbars.

5. A'structure including a cartridge type high current-carrying capacityfuse comprising a cylindrical casing having a relatively largecrosssectional area and a pair of cylindrical connector studs having arelatively small cross-sectional area arranged coaxially with respect tosaid casing and projecting from opposite ends thereof and a fuse holdercomprising a pair of substantially L-shaped brackets, each of said pairof brackets being arranged with one shank thereof in a pair of parallelplanes spaced a distance slightly in excess of the length of said casingof said fuse, and each of said pair of brackets being arranged withanother shank thereof in a common plane, each shank of said pairofbrackets arranged in said pair of parallel planes being formed by asubstantially equilateral substantially square block substantially equalin length to the diameter of said casing of said fuse, said blockforminga divided bearing substantially equal in diameter to the diameter of oneof said pair of connector studs of said fuse and in cooperativeengagement with said one of said pair of connector studs, each shank ofsaid pair of brackets arranged in said common plane being provided with,a plurality of transverse bores adapted'for attachment thereof to asystem of spaced bus bars.

6. A structure including a cartridge type high current-carrying capacityfuse comprising a casing having a relatively large cross-sectional areaand a pair of coaxial cylindrical connector studs having a relativelysmall cross-sectional area projecting from opposite ends of said casing,said pair of connector studs being hollow at least in part to increasethe ratio of surface to crosssectional area thereof, and a fuse holderadapted to receive said pair of connector studs, said fuse holdercomprising two spaced fuse supports each forming a divided bearinghaving a cylindrical bearing surface in cooperative engagement with oneof said pair of connector studs and each having clamping screws forfirmly clamping said bearing surface against one of said pair ofconnector studs in a direction transversely of said pair of connectorstuds.

7. A structure including a cartridge type high current-carrying capacityfuse comprising a cylindrical 'c'asinghaving a relatively largecrosssectional area and a pair of cylindrical connector studs having arelatively small cross-sectional area arranged coaxially with respect tosaid casing and projecting from opposite ends thereof, said pair ofconnector studs being hollow at least in part to increase the ratio ofsurface to crosssectional area thereof, and a fuse holder oomprising apair of substantially L-shaped brackets, each of said pair of bracketsbeing arranged with one shank thereof in a pair of parallel planesspaced a distance slightly in excess of the length of said spaced casingof said fuse, each of said pair of brackets being arrangecl'with anothershank thereof in a common plane, each shank of said pair of bracketsarranged in said pair of parallel planes being formed by a substantiallyequilateral square block substantially equal in length to the diameterof said casing of said fuse, said block forming a divided bearingsubstantially equal in diameter to the diameter of one of said pair ofconnector studs and in cooperative engagement with said one of said pairof connector studs, each shank of said pair of brackets arranged in saidcommon plane being provided with a plurality of transverse bores adaptedfor attachment thereof to a system of spaced bus bars.

8. A structure including a cartridge type high current-carrying capacityfuse comprising a casing having a relatively large cross-sectional areaand a pair of coaxial cylindrical connector studs having a relativelysmall cross-sectional area projecting from opposite ends of said casing,and a pair of solid metal blocks each defining a sleeve for receivingone of said pair of connector studs, each of said pair of metal blocksbeing divided by a slit extending radially with respect to said pair ofconnector studs and each said pair of metal blocks being provided with apair of clamping screws arranged symmetrically with respect to thecommon axis of said pair of connector studs and at right angles withrespect to said slit in each of said pair of metal blocks to press eachof said pair of metal blocks against one of said pair of connectorstuds.

FREDERICK J. KOZACKA.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 746,050 Downes Dec. 8, 1903 1,197,957 Sachs Sept. 12, 1916

